Though its name sounds better suited to fantasy or sci-fi,
researchers have recently gathered evidence that something called dark
lightning exists, the Washington Post reported.

Like any evil twin, dark lightning appears to "compete" with the ordinary lightning during thunderstorms.

A person could be struck by dark lightning and not even know it.

Like ordinary lightning, dark lightning brews inside thunderclouds.
In fact, it may be a competing way for the clouds to release their
energy, says Joseph Dwyer, a lightning researcher at the Florida
Institute of Technology. Dwyer has come up with a model explaining how
dark lightning arises. His idea awaits further measurements for
confirmation.

Scientists first began seeing hints of dark lightning from gamma ray measurements from satellites since at least the 1990s, according to this NASA video.
Gamma rays, the most energetic wave in the electromagnetic spectrum,
are typically associated with radioactive decay, nuclear detonations and
supernova explosions. Dark lightning appears to be made of X-rays and
gamma rays.